1. Technical Field of the Present Invention
The present invention generally relates to voltage islands, and more specifically, to methods and apparatuses that transmit signals across such voltage islands.
2. Description of Related Art
The semiconductor industry is constantly increasing the number of circuits and functionality that can be compressed onto a single die. As process dimensions decrease, this ability has grown at an astronomical rate. The ability to put entire functioning systems on a single die is now the norm rather than the exception. As a consequence of this growth, the die/integrated circuit can be viewed as compilation of functioning islands.
Some of these islands operate at different voltages from one another, others have the ability to switch to standby or sleep mode, while still others result from the need to isolate noisy circuitry. The ability to combine these different islands onto a single integrated circuit, requires techniques and circuitry for propagating communication (clocks, signals, etc), power, and output results.
One problem associated with these types of voltage islands, results from the ability to put various islands in standby or sleep mode (xe2x80x9csleeping islandxe2x80x9d). The problem arises when a signal not associated with the sleeping island must cross the sleeping island. More specifically, when the sleeping island is large enough in size such that buffering is required to improve the signal for noise and/or performance reasons. Obviously, the buffering could occur outside the sleeping island, but this is not always desirable.
It would, therefore, be a distinct advantage if the buffering of such a signal could occur within the sleeping voltage island itself. The present invention provides such a method and apparatus.
The present invention is a method and apparatus for buffering a signal in a voltage island that is in standby or sleep mode. The apparatus uses a buffer(s) that are powered from a global power supply voltage that is always powered, and such buffer(s) are placed within the sleeping island itself. The sleeping island can be at the same or different voltage from the global voltage.